PROCEDURES FOR SAMPLING METHANE GAS INSIDE BUILDINGS

Solid Waste Management Program fact sheet

06/2014

Division of Environmental Quality Director: Leanne Tippett Mosby

PUB2052

OverviewThis document was prepared by the Missouri Department of Natural Resources’ Solid WasteManagement Program (SWMP) to provide guidance on how to properly sample for methane gases in enclosed spaces.

Sampling EquipmentProper selection of sampling equipment to be used for monitoring buildings is critical to makeproper public safety assessments. While explosimeter-type instruments are appropriate for measuring methane in most monitoring in buildings, be aware that some meters burn the sample to analyze it. In an oxygen-free environment, this type of meter is not reliable and can give methane readings that are falsely low. For monitoring of spaces that may be oxygen-free, such as manholes and underground utility vaults, oxygen levels should also be sampled for worker safety and to ensure that the methane monitoring equipment being used is appropriate to measure in these conditions. Detection instruments selected for monitoring buildings must have a detection threshold below 1.25% methane.

Step 1 - Make sure the instrument has been properly calibrated to methane (Some instruments of this type are calibrated to hexane or propane, which have different combustible limits than methane).

Step 2 - Prepare the instrument for sampling by allowing it to properly warm up per the manufacturer’s instructions.

Step 3 - Attach the hose to the instrument and begin sampling. Some instruments have wands that can be attached to the plastic hose to collect air samples. You must sample at each location for a long enough duration that the instrument will respond if methane is present. Each instrument should have a response time designated by the manufacturer that should be followed to ensure results are valid.

Step 4 - If methane is detected by the instrument in any concentration it should be recorded and reported to the department.

Sampling TimesThe times chosen to monitor methane gas are almost as important as the procedures used to collect the sample. If possible, sample collection should occur when landfill gases are most likely to migrate. Scientific evidence indicates that weather and soil conditions influence when gas will migrate. For these reasons sampling should be considered when:

Barometric pressure is low; or

Soils are saturated; or

The ground surface is frozen, snow- and/or ice-covered.

Regulatory RequirementsThe Missouri Solid Waste Management Regulations [ 10 CSR 80-3.010(14) and 10 CSR 80-4.010(14) ] require that owners of sanitary landfills in operation after January 1, 1994, and owners of demolition landfills in operation after July 30, 1997, conduct quarterly monitoring of all buildings located within the landfill’s permitted boundary. Owners of the landfills must implement a methane monitoring program to ensure that regulatory limits for methane are not exceeded - 1.25 percent (25 percent of the lower explosive limit) by volume in buildings on site. Samples must be collected at least quarterly and the results must be submitted to the SWMP in an electronic format within a week of collection. The information to be included in the data submission and the format by which to submit the data is described in the SWMP’s fact sheet, “Methane Gas Monitoring Data Submission Guidance.”

Corrective Action / Emergency ResponseIf methane gas concentrations in the structure exceed regulatory limits or are an obvious public safety threat, the landfill owner/operator must do the following:

Immediately evacuate the structure and take all necessary steps to ensure protection of public health and safety.

Notify the following:

Local fire department

Other appropriate emergency management or public health and safety authorities

The department

Owners of underground utilities within 1,000 feet of the affected structure

Take appropriate action to mitigate the effects of the methane accumulation in the affected structures until a permanent remediation is completed.

Follow the instructions of the fire department or emergency management or public health and safety authorities. This may include:

Ventilating the affected structure

Inspecting the affected structure and sampling for methane or installing methane detectors inside the structure

Sealing methane intrusion pathways into the affected structure

Implement corrective actions as necessary.

ConclusionsMissouri has stringent regulations governing methane gas migration. Landfill gases that migrate into buildings present a threat to public safety. It is the responsibility of the landfill owner/operator to take any and all steps to protect landfill employees, contract workers, visitors, and the general public from migrating landfill gases.

ReferencesFarquhar, Grahame, Monitoring and Controlling Methane Gas Migration, course notes presented at April 1993 Sanitary Landfill Design and Management training, offered by the University of Wisconsin-Madison, College of Engineering.